Publications

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Book Chapter
Cotton, WR, Walko RL, Costignan KR, Flatau PJ, Pielke RA.  1993.  Using Regional Atmospheric Modeling System n the Large Eddy Simulation mode: From in homogenous surfaces to cirrus clouds. Large eddy simulation of complex engineering and geophysical flows. ( Galperin B, Orszag SA, Eds.).:369-398., Cambridge [England]; New York, NY, USA: Cambridge University Press Abstract
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Journal Article
Wells, KC, Witek M, Flatau P, Kreidenwei SM, Westphal DL.  2007.  An analysis of seasonal surface dust aerosol concentrations in the western US (2001-2004): Observations and model predictions. Atmospheric Environment. 41:6585-6597.   10.1016/j.atmosenv.2007.04.034   AbstractWebsite

Long-term surface observations indicate that soil dust represents over 30% of the annual fine (particle diameter less than 2.5 mu m) particulate mass in many areas of the western US; in spring and summer, it represents an even larger fraction. There are numerous dust-producing playas in the western US, but surface dust aerosol concentrations in this region are also influenced by dust of Asian origin. This study examines the seasonality of surface soil dust concentrations at 15 western US sites using observations from the Interagency Monitoring of PROtected Visual Environments (IMPROVE) network from 2001 to 2004. Average soil concentrations in particulate matter less than 10 mu m in diameter (PM 10) were lowest in winter and peaked during the summer months at these sites; however, episodic higher-concentration events (> 10 mu g m(-3)) occurred in the spring, the time of maximum Asian dust transport to the western US. Simulated surface dust concentrations from the Navy Aerosol Analysis and Prediction System (NAAPS) suggested that long-range transport from Asia dominates surface dust concentrations in the western US in the spring, and that, although some long-range transport does occur throughout the year (1-2 mu g m(-3)), locally generated dust plays a larger role in the region in summer and fall. However, NAAPS simulated some anomalously high concentrations (> 50 mu g m(-3)) of local dust in the fall and winter months over portions of the western US. Differences between modeled and observed dust concentrations were attributed to overestimation of total observed soil dust concentrations by the assumptions used to convert IMPROVE measurements into PM(10) soil concentrations, lack of inhibition of model dust production in snow-covered regions, and lack of seasonal agricultural sources in the model. (c) 2007 Elsevier Ltd. All rights reserved.

Markowicz, KM, Flatau PJ, Kardas AE, Remiszewska J, Stelmaszczyk K, Woeste L.  2008.  Ceilometer retrieval of the boundary layer vertical aerosol extinction structure. Journal of Atmospheric and Oceanic Technology. 25:928-944.   10.1175/2007jtecha1016.1   AbstractWebsite

The CT25K ceilometer is a general-purpose cloud height sensor employing lidar technology for detection of clouds. In this paper it is shown that it can also be used to retrieve aerosol optical properties in the boundary layer. The authors present a comparison of the CT25K instrument with the aerosol lidar system and discuss its good overall agreement for both the range-corrected signals and the retrieved extinction coefficient profiles. The CT25K aerosol profiling is mostly limited to the boundary layer, but it is capable of detecting events in the lower atmosphere such as mineral dust events between 1 and 3 km. Assumptions needed for the estimation of the aerosol extinction profiles are discussed. It is shown that, when a significant part of the aerosol layer is in the boundary layer, knowledge of the aerosol optical depth from a sun photometer allows inversion of the lidar signal. In other cases, surface observations of the aerosol optical properties are used. It is demonstrated that additional information from a nephelometer and aethalometer allows definition of the lidar ratio. Extinction retrievals based on spherical and randomly oriented spheroid assumptions are performed. It is shown, by comparison with the field measurements during the United Arab Emirates Unified Aerosol Experiment, that an assumption about specific particle shape is important for the extinction profile inversions. The authors indicate that this limitation of detection is a result of the relatively small sensitivity of this instrument in comparison to more sophisticated aerosol lidars. However, in many cases this does not play a significant role because globally only about 20% of the aerosol optical depth is above the boundary layer.

Markowicz, KM, Flatau PJ, Vogelmann AM, Quinn PK, Welton EJ.  2003.  Clear-sky infrared aerosol radiative forcing at the surface and the top of the atmosphere. Quarterly Journal of the Royal Meteorological Society. 129:2927-2947.   10.1256/qj.02.224   AbstractWebsite

We study the aerosol radiative forcing at infrared (IR) wavelengths using data from the Aerosol Characterization Experiment. ACE-Asia, cruise of the National Oceanic and Atmospheric Administration research vessel Ronald H. Brown. The analyses apply to the daytime periods of clear-sky conditions for the area within the immediate vicinity of the ship. An optical model is derived from chemical measurements, lidar profiles, and visible-extinction measurements, which are used to estimate the IR aerosol optical thickness and the single-scattering albedo. The IR model results are compared to detailed Fourier transform interferometer-based IR aerosol forcing estimates, pyrgeometer-based IR downward fluxes, and to observations of the direct aerosol solar forcing. This combined approach attests to the self-consistency of the optical model, and allows us to derive quantities such as the IR forcing at the top of the atmosphere (TOA) and the IR optical thickness. The mean IR aerosol optical thickness at 10 mum is 0.08 and the single-scattering albedo is 0.55. The modelled IR aerosol surface forcing reaches 10 W m(-2) during the cruise, which is a significant contribution compared to the total direct aerosol forcing. The surface IR aerosol radiative forcing is between 10 and 25% of the short-wave aerosol forcing. The IR aerosol forcing at the TOA can be up to 19% of the solar aerosol forcing. We show good agreement between TOA aerosol IR forcing derived from the model and from the CERES (Clouds and the Earth's Radiant Energy System) satellite data. Over the Sea of Japan, the average IR aerosol radiative forcing is 4.6 W m(-2) at the surface. and 1.5 W m(-2) at the TOA. The IR forcing efficiency at the TOA is a strong function of aerosol temperature (which is coupled to vertical structure) and changes between 10 and 18 W m(-2) (per IR optical depth unit), while the surface IR forcing efficiency varies between 37 and 55 W m(-2) (per IR optical depth unit).

Witek, ML, Flatau PJ, Teixeira J, Westphal DL.  2007.  Coupling an ocean wave model with a global aerosol transport model: A sea salt aerosol parameterization perspective. Geophysical Research Letters. 34   10.1029/2007gl030106   AbstractWebsite

[1] A new approach to sea salt parameterization is proposed which incorporates wind- wave characteristics into the sea salt emission function and can be employed globally and under swell- influenced conditions. The new source function was applied into Navy Aerosol Analysis and Prediction System model together with predictions from the global wave model Wave Watch III. The squared surface wind velocity U-10 and the wave's orbital velocity V-orb= pi H-s/ T-P are shown to be the key parameters in the proposed parameterization. Results of the model simulations are validated against multi- campaign shipboard measurements of the sea salt aerosol. The validations indicate a good correlation between V-orb and the measured surface concentrations. The model simulations with the new parameterization exhibit an improved agreement with the observations when compared to a wind- speed- only approach. The proposed emission parameterization has the potential to improve the simulations of sea salt emission in aerosol transport models.

Collins, WD, Bucholtz A, Flatau P, Lubin D, Valero FPJ, Weaver CP, Pilewski P.  2000.  Determination of surface heating by convective cloud systems in the central equatorial Pacific from surface and satellite measurements. Journal of Geophysical Research-Atmospheres. 105:14807-14821.   10.1029/2000jd900109   AbstractWebsite

The heating of the ocean surface by longwave radiation from convective clouds has been estimated using measurements from the Central Equatorial Pacific Experiment (CEPEX). The ratio of the surface longwave cloud forcing to the cloud radiative forcing on the total atmospheric column is parameterized by the f factor. The f factor is a measure of the partitioning of the cloud radiative effect between the surface and the troposphere. Estimates of the f factor have been obtained by combining simultaneous observations from ship, aircraft, and satellite instruments. The cloud forcing near the ocean surface is determined from radiometers on board the National Oceanic and Atmospheric Administration P-3 aircraft and the R/V John Vickers. The longwave cloud forcing at the top of the atmosphere has been estimated from data obtained from the Japanese Geostationary Meteorological Satellite GMS 4. A new method for estimating longwave fluxes from satellite narrowband radiances is described. The method is based upon calibrating the satellite radiances against narrowband and broadband infrared measurements from the high-altitude NASA ER-2 aircraft. The average value of f derived from the surface and satellite observations of convective clouds is 0.15 +/- 0.02. The area-mean top-of-atmosphere longwave forcing by convective clouds in the region 10 degrees S-10 degrees N, 160 degrees E-160 degrees W is 40 W/m(2) during CEPEX. Those results indicate that the surface longwave forcing by convective clouds was approximately 5 W/m(2) in the central equatorial Pacific and that this forcing is the smallest radiative component of the surface energy budget.

Lelieveld, J, Berresheim H, Borrmann S, Crutzen PJ, Dentener FJ, Fischer H, Feichter J, Flatau PJ, Heland J, Holzinger R, Korrmann R, Lawrence MG, Levin Z, Markowicz KM, Mihalopoulos N, Minikin A, Ramanathan V, de Reus M, Roelofs GJ, Scheeren HA, Sciare J, Schlager H, Schultz M, Siegmund P, Steil B, Stephanou EG, Stier P, Traub M, Warneke C, Williams J, Ziereis H.  2002.  Global air pollution crossroads over the Mediterranean. Science. 298:794-799.   10.1126/science.1075457   AbstractWebsite

The Mediterranean Intensive Oxidant Study, performed in the summer of 2001, uncovered air pollution layers from the surface to an altitude of 15 kilometers. In the boundary layer, air pollution standards are exceeded throughout the region, caused by West and East European pollution from the north. Aerosol particles also reduce solar radiation penetration to the surface, which can suppress precipitation. In the middle troposphere, Asian and to a lesser extent North American pollution is transported from the west. Additional Asian pollution from the east, transported from the monsoon in the upper troposphere, crosses the Mediterranean tropopause, which pollutes the lower stratosphere at middle latitudes.

Witek, ML, Flatau PJ, Quinn PK, Westphal DL.  2007.  Global sea-salt modeling: Results and validation against multicampaign shipboard measurements. Journal of Geophysical Research-Atmospheres. 112   10.1029/2006jd007779   AbstractWebsite

[1] Open-ocean measurements of sea-salt concentrations from five different campaigns are used to validate the sea-salt parameterization in numerical models. The data set is unique in that it is from open-ocean shipboard measurements which alleviates typical problems associated with onshore wave breaking on land stations ( surf zone). The validity of the sea-salt parameterizations is tested by employing a global forecasting model and transport model with detailed representation of dry and wet deposition, advection and diffusion, and other physical processes. It is shown that the inclusion of these processes leads to good agreement with shipboard measurements. The correlation coefficient of measured and modeled sea-salt mass concentrations for all data points was 0.76 and varied from 0.55 to 0.84 for different experiments. Average sea-salt mass concentration was 4.6 mu g/m(3) from measurements and 7.3 mu g/m(3) from the model, for all considered experiments. It was found that model-measurements discrepancies were affected by wet deposition uncertainties but also suggested was the influence of source uncertainties in the strong wind-speed regime, lack of a wind-speed threshold for emission onset, and lack of size differentiation in applied deposition velocity. No apparent relationship between the water temperature and the measured sea-salt concentration was found in the analyzed data set.

Welton, EJ, Voss KJ, Quinn PK, Flatau PJ, Markowicz K, Campbell JR, Spinhirne JD, Gordon HR, Johnson JE.  2002.  Measurements of aerosol vertical profiles and optical properties during INDOEX 1999 using micropulse lidars. Journal of Geophysical Research-Atmospheres. 107   10.1029/2000jd000038   AbstractWebsite

[1] Micropulse lidar (MPL) systems were used to measure aerosol properties during the Indian Ocean Experiment (INDOEX) 1999 field phase. Measurements were made from two platforms: the NOAA ship R/V Ronald H. Brown, and the Kaashidhoo Climate Observatory (KCO) in the Maldives. Sun photometers were used to provide aerosol optical depths (AOD) needed to calibrate the MPL. This study focuses on the height distribution and optical properties (at 523 nm) of aerosols observed during the campaign. The height of the highest aerosols (top height) was calculated and found to be below 4 km for most of the cruise. The marine boundary layer (MBL) top was calculated and found to be less than 1 km. MPL results were combined with air mass trajectories, radiosonde profiles of temperature and humidity, and aerosol concentration and optical measurements. Humidity varied from approximately 80% near the surface to 50% near the top height during the entire cruise. The average value and standard deviation of aerosol optical parameters were determined for characteristic air mass regimes. Marine aerosols in the absence of any continental influence were found to have an AOD of 0.05+/-0.03, an extinction-to-backscatter ratio (S ratio) of 33+/-6 sr, and peak extinction values around 0.05 km(-1) (near the MBL top). The marine results are shown to be in agreement with previously measured and expected values. Polluted marine areas over the Indian Ocean, influenced by continental aerosols, had AOD values in excess of 0.2, S ratios well above 40 sr, and peak extinction values approximately 0.20 km(-1) (near the MBL top). The polluted marine results are shown to be similar to previously published values for continental aerosols. Comparisons between MPL derived extinction near the ship (75 m) and extinction calculated at ship level using scattering measured by a nephelometer and absorption using a particle soot absorption photometer were conducted. The comparisons indicated that the MPL algorithm (using a constant S ratio throughout the lower troposphere) calculates extinction near the surface in agreement with the ship-level measurements only when the MBL aerosols are well mixed with aerosols above. Finally, a review of the MPL extinction profiles showed that the model of aerosol vertical extinction developed during an earlier INDOEX field campaign (at the Maldives) did not correctly describe the true vertical distribution over the greater Indian Ocean region. Using the average extinction profile and AOD obtained during marine conditions, a new model of aerosol vertical extinction was determined for marine atmospheres over the Indian Ocean. A new model of aerosol vertical extinction for polluted marine atmospheres was also developed using the average extinction profile and AOD obtained during marine conditions influenced by continental aerosols.

Conant, WC, Seinfeld JH, Wang J, Carmichael GR, Tang YH, Uno I, Flatau PJ, Markowicz KM, Quinn PK.  2003.  A model for the radiative forcing during ACE-Asia derived from CIRPAS Twin Otter and R/V Ronald H. Brown data and comparison with observations. Journal of Geophysical Research-Atmospheres. 108   10.1029/2002jd003260   AbstractWebsite

Vertical profiles of aerosol size, composition, and hygroscopic behavior from Center for Interdisciplinary Remotely Piloted Aircraft Studies (CIRPAS) Twin Otter and National Oceanic and Atmospheric Administration R/V Ronald H. Brown observations are used to construct a generic optical model of the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) aerosol. The model accounts for sulfate, black carbon, organic carbon, sea salt, and mineral dust. The effects of relative humidity and mixing assumptions (internal versus external, coating of dust by pollutants) are explicitly accounted for. The aerosol model is integrated with a Monte Carlo radiative transfer model to compute direct radiative forcing in the solar spectrum. The predicted regional average surface aerosol forcing efficiency (change in clear-sky radiative flux per unit aerosol optical depth at 500 nm) during the ACE-Asia intensive period is -65 Wm(-2) for pure dust and -60 Wm(-2) for pure pollution aerosol (clear skies). A three-dimensional atmospheric chemical transport model (Chemical Weather Forecast System (CFORS)) is used with the radiative transfer model to derive regional radiative forcing during ACE-Asia in clear and cloudy skies. Net regional solar direct radiative forcing during the 5-15 April 2001 dust storm period is -3 Wm(-2) at the top of the atmosphere and -17 Wm(-2) at the surface for the region from 20degreesN to 50degreesN and 100degreesE to 150degreesE when the effects of clouds on the direct forcing are included. The model fluxes and forcing efficiencies are found to be in good agreement with surface radiometric observations made aboard the R. H. Brown. Mean cloud conditions are found to moderate the top of atmosphere (TOA) radiative forcing by a factor of similar to3 compared to clear-sky calculations, but atmospheric absorption by aerosol is not strongly affected by clouds in this study. The regional aerosol effect at the TOA ("climate forcing") of -3 Wm(-2) is comparable in magnitude, but of opposite sign, to present-day anthropogenic greenhouse gas forcing. The forcing observed during ACE-Asia is similar in character to that seen during other major field experiments downwind of industrial and biomass black carbon sources (e.g., the Indian Ocean Experiment (INDOEX)), insofar as the primary effect of aerosol is to redistribute solar heating from the surface to the atmosphere.

Remiszewska, J, Flatau PJ, Markowicz KM, Reid EA, Reid JS, Witek ML.  2007.  Modulation of the aerosol absorption and single-scattering albedo due to synoptic scale and sea breeze circulations: United Arab Emirates experiment perspective. Journal of Geophysical Research-Atmospheres. 112   10.1029/2006jd007139   AbstractWebsite

The spectral aerosol absorption properties in the Arabian Gulf region were observed during the United Arab Emirates Unified Aerosol Experiment (UAE(2)). Measurements were taken at a coastal region of the Arabian Gulf located 60 km northeast of Abu Dhabi, the capital of the United Arab Emirates, allowing characterization of pollution and dust absorption properties in a highly heterogeneous environment. A large observed change of the diurnal signal during the period under study ( 27 August through 30 September 2004) was due to ( 1) strong sea and land breeze and ( 2) changes in prevailing synoptic-scale flow. During the night, stagnating air resulted in gradual accumulation of pollution with maximum absorption in the early morning hours. The rising sun increased both the depth of the boundary layer and the temperature of the interior desert, resulting in strong and sudden sea breeze onset which ventilated the polluted air accumulated during the night. Our observations show that the onshore winds brought cleaner air resulting in decreasing values of the absorption coefficient and increasing values of the single-scattering albedo (SSA). The mean value of the absorption coefficient at 550 nm measured during the sea breeze was 10.2 +/- 0.9 Mm(-1), while during the land breeze it was 13.8 +/- 1.2 Mm(-1). Synoptic- scale transport also strongly influenced particle fine/ coarse partition with "northern'' flow bringing pollution particles and "southern'' flow bringing more dust.

Witek, ML, Flatau PJ, Teixeira J, Markowicz KM.  2011.  Numerical Investigation of Sea Salt Aerosol Size Bin Partitioning in Global Transport Models: Implications for Mass Budget and Optical Depth. Aerosol Science and Technology. 45:401-414.   10.1080/02786826.2010.541957   AbstractWebsite

In this study the importance of sea salt aerosol (SSA) size representation in a global transport model is investigated. For this purpose the Navy Aerosol Analysis and Prediction System (NAAPS) model is employed in a number of SSA simulations. A new dry deposition velocity parameterization is implemented into NAAPS in order to more physically represent deposition processes in the model. SSA size distribution is divided into size bins using two different partition procedures: the previously used iso-log method and the iso-gradient method, which relies on size-dependence of deposition processes. The global SSA simulations are analyzed in terms of the total sea salt mass and the average SSA optical thickness. The results indicate that there is a large dependence of the total mass and average aerosol optical depth on the number of size bins used to represent the aerosol size distribution. The total SSA mass is underestimated by 20% if 2 instead of 15 (reference) size intervals are used. The average aerosol optical depth underestimation is even higher and reaches over 35%. Such large differences can have substantial implications on the accuracy of SSA radiative forcing simulations in climate models. A comparison of the two division procedures shows that the simulations with the iso-gradient intervals are more accurate than the iso-log ones if at least 6 size bins are used. This result indicates that the more physically based division scheme can offer better performance and reduce computational cost of global aerosol transport models.

Markowicz, KM, Flatau PJ, Remiszewska J, Witek M, Reid EA, Reid JS, Bucholtz A, Holben B.  2008.  Observations and modeling of the surface aerosol radiative forcing during UAE(2). Journal of the Atmospheric Sciences. 65:2877-2891.   10.1175/2007jas2555.1   AbstractWebsite

Aerosol radiative forcing in the Persian Gulf region is derived from data collected during the United Arab Emirates (UAE) Unified Aerosol Experiment (UAE(2)). This campaign took place in August and September of 2004. The land -sea-breeze circulation modulates the diurnal variability of the aerosol properties and aerosol radiative forcing at the surface. Larger aerosol radiative forcing is observed during the land breeze in comparison to the sea breeze. The aerosol optical properties change as the onshore wind brings slightly cleaner air. The mean diurnal value of the surface aerosol forcing during the UAE2 campaign is about -20 W m(-2), which corresponds to large aerosol optical thickness (0.45 at 500 nm). The aerosol forcing efficiency [i. e., broadband shortwave forcing per unit optical depth at 550 nm, W m(-2) (tau(500))(-1)] is -53 W m(-2) (tau(500))(-1) and the average single scattering albedo is 0.93 at 550 nm.

Witek, ML, Teixeira J, Flatau PJ.  2008.  On stable and explicit numerical methods for the advection-diffusion equation. Mathematics and Computers in Simulation. 79:561-570.   10.1016/j.matcom.2008.03.001   AbstractWebsite

In this paper two stable and explicit numerical methods to integrate the one-dimensional (1D) advection-diffusion equation are presented. These schemes are stable by design and follow the main general concept behind the semi-Lagrangian method by constructing a virtual grid where the explicit method becomes stable. It is shown that the new schemes compare well with analytic solutions and are often more accurate than implicit schemes. In particular, the diffusion-only case is explored in some detail. The error produced by the stable and explicit method is a function of the ratio between the standard deviation an of the initial Gaussian state and the characteristic virtual grid distance AS. Larger values of this ratio lead to very accurate results when compared to implicit methods, while lower values lead to less accuracy. It is shown that the sigma(0)/Delta S ratio is also significant in the advection-diffusion problem: it determines the maximum error generated by new methods, obtained with a certain combination of the advection and diffusion values. In addition, the error becomes smaller when the problem becomes more advective or more diffusive. (C) 2008 IMACS. Published by Elsevier B.V. All rights reserved.

Stramski, D, Wozniak SB, Flatau PJ.  2004.  Optical properties of Asian mineral dust suspended in seawater. Limnology and Oceanography. 49:749-755. AbstractWebsite

The spectral optical properties of Asian mineral dust suspended in seawater exhibit significant variability associated with the origin (and, hence, the chemistry and mineralogy) and particle size distribution of the samples. The measurements of dust samples from different locations show that the mass-specific absorption coefficient of particles, a(p)*, at a wavelength of light lambda = 440 nm, varies from about 0.028 m(2) g(-1) for the soil dust from Chinese desert Pnear Dunhuang to 0.15 m(2) g(-1) for the soil dust of volcanic origin in Cheju Island (South Korea). At lambda = 400 nm, this range is 0.05-0.23 m(2) g(-1). The aerosol sample collected in the Sea of Japan during a massive dust storm in East Asia shows a(p)*(lambda) > 0.1 m(2) g(-1) for lambda < 425 nm. The mass-specific scattering coefficient, b(p)*(lambda), ranges from about 0.8 to 1.5 m(2) g(-1) at blue and green wavelengths for the samples examined. The single scattering albedo, omega(0) increases with wavelength. For lambda > 400 nm, omega(0) was > 0.78 for the sample from Cheju Island and > 0.9 for other samples. In the near-infrared region (750-850 nm), where absorption by dust particles is small or undetectable, omega(0), was close to 1.

Flatau, PJ, Walko RL, Cotton WR.  1992.  Polynomial Fits to Saturation Vapor-Pressure. Journal of Applied Meteorology. 31:1507-1513.   10.1175/1520-0450(1992)031<1507:pftsvp>2.0.co;2   AbstractWebsite

The authors describe eighth- and sixth-order polynomial fits to Wexler's and Hyland-Wexler's saturation-vapor-pressure expressions. Fits are provided in both least-squares and relative-error norms. Error analysis is presented. The authors show that their method is faster in comparison with the reference expressions when implemented on a CRAY-YMP.